Drilling tools are used to drill cylindrical holes in metallic workpieces. The cutting or boring action of the drill tools may be carried out by an elongated, substantially cylindrical drilling tool, such as a combination of a tool holder and a drill insert, which is selectively attached thereto. Such an arrangement may then be used in an application wherein one end of the tool holder is securely mounted in a driving apparatus, which rotates the holder about its longitudinal axis. At the opposite end of the elongated tool holder, the cutting insert engages the material to be cut. Alternatively, the workpiece may be made to rotate relative to the holder and cutting insert, such as in positioning the holder in the tail stock of a lathe or the like. Further, tool and workpiece can be made to rotate relative to one another. The use of cutting inserts allows for quick changing of the insert upon wear of the cutting surfaces instead of the entire tool, and allows for one tool to be used for a variety of different boring applications by simply changing the insert and not the entire drill assembly.
The indexable drill inserts plays a very important role in drilling because all the sides of insert can be used for cutting one after the other. Further, use of inserts reduces the manufacturing lead time and assembling time.
The use of quadrangular indexable drill inserts is known in the art. However, the inserts which are in the art comprises four rectangular cutting edges for cutting the workpiece. The use of rectangular cutting edges make the drill tend to drift away from its center because the cutting forces act all over the drill body and not exactly at the center. The drill drift further creates a narrow wall which is not feasible in practical applications. Further, conventional indexable drill inserts rub the surface of the drilling hole if the diameter of the drill hole is less than the predetermined value.
Recently, many techniques have been introduced by various drill insert manufactures to balance the cutting forces in the drill body to prevent a drill from drifting from the center. One such technique is to divide the cutting edge into a plurality of part edges. The part edges are oriented in a predetermined pattern to balance the cutting forces. In the conventional drill inserts the part edges are joined by a transition edge comprising a convex curve and a concave curve. The chip formation in the conventional cutting inserts is unsmooth since there is a sudden change over from the concave portion to the convex portion, which results in a high stress area. Also, the chips may sometimes split themselves into smaller fragments, which instead of getting into the flute of the drill tool, go around the drill tool, thereby ruining the surface finish of the hole produced.
In light of the foregoing discussion, it is necessary to develop a drill insert to overcome the limitations of the prior art stated in the above background.